3.8 Important drug interactions

Concomitant administration of a benzodiazepine with a drug which is sedative (eg alcohol) or which reduces blood pressure (eg ACE inhibitor) can increase the potential for these effects.

Consult summaries of product characteristics and other sources of information on the interactions of individual benzodiazepines.

Interacting drug or drug class	Effect of interaction	Risk-reduction measures
Drugs that reduce blood pressure: ACE inhibitors and angiotensin-II receptor antagonists Alpha1 adrenoceptor antagonists (eg alfuzosin, doxazosin, indoramin, prazosin, tamsulosin, terazosin) Beta-blockers Calcium-channel blockers Clonidine Diazoxide Diuretics (thiazide eg bendroflumethiazide and loop eg furosemide) Methyldopa Moxonidine Nitrates (glyceryl trinitrate, isosorbide dinitrate, isosorbide mononitrate)	Increased hypotensive effect	Monitor blood pressure
Drugs that cause sedation(either as their primary effect or as an unwanted effect): Alcohol Anaesthetics, general Antidepressants (including tricyclic antidepressants and mirtazapine) Antihistamines¹, sedative Antipsychotics Lofexidine Moxonidine Opioid analgesics Tizanidine	Increased sedation and increased risk of respiratory depression and hypotension. Combined disinhibitory²effects of alcohol and a benzodiazepine may increase the possibility of aggressive behaviour.	Warn individual of excessive sedation and psychomotor³impairment. Effects on respiration and blood pressure may need to be monitored when initiating treatment or increasing the dose.
Baclofen	Increased sedation	Warn individual of excessive sedation and psychomotor⁴impairment
Cimetidine	Benzodiazepine effect increased
Disulfiram	Benzodiazepine effect increased
Enzyme-inducing drugs such as: Carbamazepine Phenobarbital Rifampicin	Enzyme induction may reduce benzodiazepine effect
Levodopa	Antiparkinsonian effect of levodopa may be reduced rarely
Phenytoin	Benzodiazepines may raise or lower the concentration of phenytoin in blood
Ritonavir	Effect of benzodiazepine increased—risk of excessive CNS depression	Avoid concomitant use, especially of alprazolam, diazepam and flurazepam
Sodium oxybate	Effect of sodium oxybate increased	Avoid concomitant use of a benzodiazepine and sodium oxybate

A substance that blocks the effects of histamine. Histamine is released when the body mounts an immune response and it is responsible for many allergy-related symptoms↩
Loss of inhibition which can lead to lack of restraint and disregard for social conventions↩
Level of consciousness or cognitive ability linked to motor behaviour↩
Level of consciousness or cognitive ability linked to motor behaviour↩